BENTONVILLE, Arkansas  Wal-Mart Stores Inc. and Tyson Foods Inc. agreed this week to participate in an emissions reduction program through the Environmental Protection Agency (EPA).

The EPA-sponsored SmartWay Transport Partnership asks members of the freight industry to voluntarily adjust their shipping operations to improve air quality and help the companies save money on fuel and shipping costs.

Companies participating in the 8-month-old federal program update technology, alter trucks to improve vehicle gas mileage and create idle-free areas to encourage truckers to cut their engines to reduce emissions.

Idle-free areas are zones in which truckers do not allow their rigs to keep running while the truck is stopped for a significant amount of time. To encourage truckers to kill their engines, companies equip truck stops with air conditioning, heat, and power for appliances  reasons truckers typically leave their trucks running. The stops are also furnished with Internet access and other amenities to entice truckers.

The companies foot the bill for the modifications, but the EPA asserts that the changes, while ultimately helping the environment, will save companies money by reducing fuel consumption.

Nationally, truck idling is blamed for the emission of 11 million tons of carbon dioxide, 180,000 tons of nitrogen oxides and 5,000 tons of particulate matter each year, according to an EPA news release.

The program's goal is to ultimately eliminate 33 million metric tons to 66 million metric tons of carbon dioxide emissions and up to 200,000 tons of nitrogen oxides by 2012  the equivalent of taking about 12 million cars off the road.

In Arkansas, officials hope SmartWay will reduce emissions by 2,500 tons of carbon dioxide, 35 tons of nitrogen oxide, and one ton of particulate matter each year.